Flat-panel displays are widely used in conjunction with computing devices, in portable devices, and for entertainment devices such as televisions. Such displays typically employ a plurality of pixels distributed over a display substrate to display images, graphics, or text. Both light-reflective and light-emissive displays are known. Light-emissive displays emit light and can be used in a dark ambient surround. In contrast, reflective displays cannot typically be viewed without incident ambient light. A variety of reflective displays are known, including reflective liquid crystal displays and electrophoretic displays, and are generally found in low-power applications such as e-readers.
In some reflective displays, a front light is integrated around the edge of the reflective display to illuminate the display so that it can be read in an otherwise dark environment. For example, U.S. Pat. Nos. 6,340,999 and 6,650,382 disclose an LCD with a front light having light sources around the edge of the display and a light guide for directing the edge lighting toward the display. U.S. Patent Application Publication No. 2004/0080483 describes a touch-panel integrated reflection-type LCD with a front light also having light sources around the edge of the display and a light guide for directing the edge lighting toward the display. U.S. Pat. No. 8,596,846 discloses an LCD with a holographic front light guide illuminated with lasers. These front-light structures require wave guides to provide uniform illumination over the display viewing surface, adding cost and thickness to the device, and are not readily integrated with touch screens. Moreover, edge illumination inhibits local dimming for rectangular areas within a subset of a display.
There remains a need, therefore, for alternative front-light structures that reduce layers in the display and are readily integrated with touch screens.